Field of Invention
The present invention relates to an intervertebral implant, and more particularly to an intervertebral implant formed of a plurality of metal balls having a uniform particle diameter; the intervertebral implant has a number of areas, where each area is formed with a different porosity and pore size based on a different forming quantity of metal balls, making the intervertebral implant a composite pore structure having multiple stiffness.
Related Art
Lumbar interbody fusion is to remove an intervertebral disc from two cervical vertebrae and then to fuse the two cervical vertebrae. Such a step is also referred to as “spinal fusion”, and is usually used for treating patients suffering from continuous back pain, sciatica or fatigue and weakness of two legs caused by spinal diseases such as spondylosis and intervertebral disc herniation.
An existing intervertebral fusion implant has problems such as an undesirable fusion effect and dislocation after bone implantation. Therefore, auxiliary treatment methods such as artificial bones, growth factors, and drugs are often utilized clinically to improve a degree of fusion of a cervical vertebra bone and an implant. However, in the case of utilizing additional adding manners, the manners have problems such as a short release period and uneven concentration in local areas. Therefore, a porous structure is arranged on an implant to enable bone growth in pores to improve a degree of fusion of the implant in a bone.
In the prior art, for example, a human cervical interbody fusion device using bioactive porous titanium alloy is disclosed in China Patent No. 202086620. The human cervical interbody fusion device using bioactive porous titanium alloy has regular pores at the circumferential portion, the average pore diameter being 300 μm to 400 μm, and the porosity being 40% to 50%; but has bony trabeculae-form irregular pores at the central portion, the average pore diameter being 400 μm to 1000 μm, and the porosity being 60% to 80%. rhBMP-2 or gelatin microspheres are attached in pores between the circumferential portion and the central portion. The porous structure and a bioactive factor sustained release system inside the porous structure can induce growth of new bone tissues, which solves the problem of fusion of a bone and a material interface, and achieves higher mechanical compatibility and bone integration capability than those of a dense material. However, for the central portion that has bony trabeculae-form irregular pores, such a structure is difficult to form. Currently metal-powder laser-sintering forming equipment still cannot achieve joint between an irregular inner portion and a regular outer portion, and pore sizes are uneven, resulting in that different stresses are easily generated in the structure.
In the prior art, for example, a gel injection molding fabrication method of a porous titanium-cobalt alloy medical implant is disclosed in China Patent No. CN101279106, which relates to the technical field of medical material fabrication. Prepare a pre-mixed solution having a concentration by using a monomer acrylamide, a cross-linking agent methylenebisacrylamide, and deionized water. Add a dispersant oleic acid to enable titanium-cobalt powder to suspend in the pre-mixed solution to prepare slurry. Adjust the pH value to 9.0 to 10.0. Next, add a suitable amount of a catalyst N-tetramethylethylenediamine and an initiator ammonium persulfat and stir the mixture even. After air removal, inject the mixture in a mould. The monomer inside the mould undergoes a polymerization reaction to form a mesh-form structure to envelope the titanium-cobalt powder, thereby forming a billet shaped by a macromolecule mesh. The billet undergoes drying, gel exclusion, and sintering to be made into a product. In addition, the porosity and mechanical performance of porous titanium-cobalt alloy may also be changed by adjusting solid content.
In the prior art, for example, a composite interbody vertebral implant for facilitating fusion of adjacent vertebrae is disclosed in U.S. Pat. No. 8,361,150 entitled Composite implant. An upper layer of a porous metal structure and a lower layer of a porous metal structure are included, and a layer of polymeric structure is positioned between the upper layer and the lower layer. The upper layer of a porous metal structure and the lower layer of a porous metal structure allow attachment and in-growth of bone cells. The middle layer of polymeric structure has an effect of adhering the upper layer of a porous metal structure and the lower layer of a porous metal structure and an effect of supporting an entire implant. The overall composite implant has the effect of achieving fusion of an upper vertebra and a lower vertebra. Such a technology is expensive; also, the upper and lower layers have a single-porosity porous structure, resulting in low stability.